Scientists in the United Kingdom have developed a new therapy in which cancer-killing viruses hide inside the immune system of mice. The researchers successfully demonstrated that macrophages (immunity-endowing white blood cells) can be used to deliver specially designed viruses that can attack tumors directly. And remarkably, the technique worked to "completely eliminate" prostate cancer in mice. As a result, clinical trials on humans could start as early as next year.

Piggybacking Viruses

The study, which was published in the journal Cancer Research, is part of a growing trend in cancer therapy: using viruses to attack tumors.

One of the early challenges in this nascent approach, however, has been in getting the viruses deep inside the tumor where they can do their work. The answer to this problem, it now appears, may come in the form of the patient's own white blood cells — which can be co-opted into kind of "trojan horse."

A primary strength of this approach is that it harnesses and bolsters the patient's own immune system to deliver the cancer-fighting virus. The researchers envision the therapy as a way to supplement traditional techniques, including chemotherapy and radiotherapy.

Riding the Surge

To make it work, Claire Lewis, a professor at the Department of Oncology in the University of Sheffield, and colleagues performed chemotherapy and radiotherapy on mice suffering from prostate cancer. As is typically the case, the therapy caused a surge in white blood cells in response to the resulting tissue damage. Macrophage-rich blood samples were then taken from the mice and supplemented with the specially engineered virus (an "oncolytic virus" [OV]).

Two days after the chemo ended, the concoction was re-injected back into the mice. Interestingly, like HIV, the virus avoided being attacked as it piggybacked aboard the macrophage. The subtly modified macrophage was accepted by the immune system and "surfed" the wave of white blood cells as it headed to the site of the tumor.

Each macrophage contained a very small number of viruses — but once inside the tumor they began to replicate. And in fact, after only 12 hours the white blood cells produced up to 10,000 viruses each, which went on to infect and destroy the cancerous cells.

By the end of the study, all mice given the new treatment showed no signs of the tumors. And according to the researchers, it completely eradicated the tumors and stopped it from growing back.